Autonomic arousal and experimentally induced pain: A critical review of the literature

BACKGROUND: Autonomic arousal frequently is assumed to be a component of the pain response, perhaps because physiological mechanisms connecting pain and autonomic reactivity can be easily conceptualized. The evidence clarifying autonomic responses specific to painful stimulation, however, has been rather sporadic and lacks coherence; thus, a summary and critical review is needed in this area. OBJECTIVES: To summarize and integrate findings from 39 experimental investigations from 1970 to 2012 of pain-induced autonomic arousal in humans. METHODS: Medline and PsycINFO databases were searched for relevant articles. References from these articles were also considered for review. RESULTS: Painful stimuli increase respiration rate, induce muscle tension, intensify electrodermal activity and dilate the pupils. Cardiovascular activity also increases, but the pattern displayed in response to pain is complex; peripheral vasoconstriction and sympathetically mediated cardiac responses are most typical. Additionally, autonomic expression of pain shows inconsistent relations with verbal and overt motor responses. CONCLUSIONS: Autonomic arousal can be legitimately measured and modified as one facet of the pain response. Future research should particularly focus on increasing sample size and broadening the diversity of participants. To improve the ability to compare and contrast findings across studies, as well as to increase the applicability of laboratory findings to naturalistic pain, investigators also must enhance experimental design by increasing uniformity or accounting for differences in methodology. Finally, further work remains to utilize more specific assessments of autonomic response and to assess relationships of autonomic reactivity with other cognitive (eg, attention) and affective (eg, anxiety) variables.